Question

1. I saw a UFO in the sky yesterday.
2. I saw a UFO in the air yesterday.
3. I saw two UFOs in the sky yesterday.
4. I saw two UFOs in the air yesterday.
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Which expressions are correct?

Answer 1

All are correct. I think we would use "sky" more than "air", but both would be correct.

Answer 2

We do say that flying objects such as airplanes, hot air balloons, helicopters, etc., are "in the air".

Answer 3

We usually say the UFO.Why you say a UFO?